This invention relates to improvements of a facing fabric for belt and a synchronous belt using the same, and specifically relates to improvements of adhesive property of the facing fabric and improvements of durability of tooth rubber layers.
A synchronous belt as a power transmission belt generally has a belt body composed of: a backing rubber layer in which a plurality of cords are embedded in a longitudinal direction of belt, and a large number of tooth rubber layers integrally provided on the backing rubber layer at regular intervals in the longitudinal direction of belt. The tooth rubber layers of the belt body are covered with a facing fabric.
In recent years, such a synchronous belt has been employed in various kinds of fields and is often used under severe conditions such as high-speed rotation, high load and high temperature. The use of the synchronous belt under such severe conditions progresses deterioration of materials forming the belt. This frequently causes, at an early stage, the tooth rubber layers to shatter or the cords to break, thereby shortening a belt life. It is therefore desired to enhance the durability of the synchronous belt.
To meet the above requirement, there have been now increasingly performed improvements of the belt body such as the use of rubber having good heat resistance for rubber forming the belt body. Out of such improvements, special attention is focused on a synchronous belt applying hydrogenated acrylonitrile-butadiene rubber (hereinafter, also referred to as "H-NBR") for rubber portion forming the belt body since H-NBR has excellent heat resistance.
Meanwhile, since the facing fabric has also a significant effect on the belt life, researches on the facing fabric have been done parallel with the researches on the belt body. For example, it is proposed to subject the facing fabric to adhesive treatment with a rubber composition in which H-NBR is mixed with silica, metylene donor, and resorcin or denatured product thereof (See Japanese Utility-Model Application Laid-Open No. 63-64948). Further, there is also proposed a facing fabric subjected to adhesive treatment with a rubber composition in which H-NBR or the like is mixed with nickel compound (See Japanese Patent Application Laid-Open No. 2-99667).
However, while each of the facing fabrics subjected to adhesive treatment with the above rubber compositions has excellent heat resistance resulting from characteristics of H-NBR and nickel compound and has a large strength maintaining ratio even after heat-aged, its adhesive property and abrasion resistance are insufficient. In particular, since a synchronous belt receives intensive stresses at tooth roots thereof, it may be broken at an early stage due to cracks generated at the tooth roots if its adhesive property and abrasion resistance are not sufficiently secured.
This invention has been made in view of the foregoing problem and has its object of enhancing not only heat resistance and the strength maintaining ratio of the facing fabric but also its abrasion resistance and its adhesive properties to rubber forming the belt body and to rubber for treating tension members such as cords, by subjecting the facing fabric to treatment with a rubber composition in which H-NBR is mixed with a specific additive. In particular, this invention has its object of preventing the belt from breaking at an early stage due to cracks generated at its tooth root to increase the belt life.